Enveloped viruses are formed by a budding process that often requires participation of host proteins. Retroviruses, rhabdoviruses, and filoviruses all use similar late domain sequences within the viral proteins to recruit host factors for budding. Although paramyxoviruses generally lack the same late domain sequences used by these viruses, we have obtained evidence that paramyxoviruses, similar to other enveloped viruses, likely recruit host factors for budding. The viral protein:host protein binding interfaces used during virus budding have the potential to be effective as targets for antiviral drug design. Hendra and Nipah viruses (Henipaviruses) are recently emerged, zoonotic paramyxoviruses that are deadly to humans. Although progress has been made in characterizing the entry mechanisms for these viruses, very little is known about mechanisms of Henipavirus budding. We propose to take advantage of our expertise in the field of paramyxovirus budding by conducting experiments with the following aims: 1. Define requirements for Henipavirus particle production. We have established virus-like particle (VLP) assembly systems for Hendra and Nipah virus. We will define which Henipavirus proteins are important for VLP production, and hence which proteins may play roles in the recruitment of host factors for budding. 2. Identify host factors involved in Henipavirus budding. Two independent strategies will be employed: co-affinity purification of host proteins from Henipavirus VLPs, and yeast two-hybrid screening. An siRNAbased secondary screen will determine which candidate binding proteins are actually important for budding. 3. Define host and viral targets for antiviral drug development. Binding interfaces between viral and host proteins will be mapped. Minimal binding fragments of host proteins will be tested for the ability to block virus budding, similar to the effect analogous fragments have on retrovirus and parainfluenza virus 5 (PIV5) budding.